Smog Help

[93 K1500]

Well Had to get the truck smogged at a test on center, passed all the emisions portions of the test but failed on the Fuel Evaporator leakdown test. Does anyone know of a good way to diagnose at home where the leak is- local shop wants 200 for just a smoke test.
Thanks

 

[TruckinAin4Sissies]

Just check the routing of your evap can hoses. Your can' might need replaced.




-Truckin'-

 

[93 K1500]

Is there a way to check the can and or tank? Maybe the seal from the pump to the tank has worn out or shifted when I changed the pump?

 

[S1I2F3]

Resurrecting an 8 year old thread, but just failed the same exact portion of smog. Sounds like a small air leak coming from top of fuel tank for my '90 stepside, but hard to tell where exactly it's coming from. For those who have done it, is it easier to pull the bed off, or drop the tank to get access?

 

[thinger2]

Resurrecting an 8 year old thread, but just failed the same exact portion of smog. Sounds like a small air leak coming from top of fuel tank for my '90 stepside, but hard to tell where exactly it's coming from. For those who have done it, is it easier to pull the bed off, or drop the tank to get access?

That really depends on your access to friends. If you have 3 more guys to help you, pull the bed. Just be aware they are real heavy.
If you are doing it by yourself, you can use the "bed tipping" method.
I've never done it on a step side buts probably about the same.
You need the factory scissor jack, 2 ratchet straps, and about 4 feet of 2x6.
The hardest part is getting the bed bolts loose.
I've done it with a 1/2 inch breaker bar.
You can do it by yourself.
Let me know if you want all the details, There are a couple of important safety tips but I'll write it all up for you.
It's all based on changing a fuel pump in the dead of night on the side of a mountain
And it works great

 

[454cid]

If you drop the tank, work on concrete and not the dirt....tanks don't balance on a jack well if the have any gas in them and the dirt wont help.

 

[S1I2F3]

Thanks all for the feedback - noticed new tanks are $90, might try to just replace that as well while I’m at it...

 

[Nonadherentguy]

Well without a evap tester or 5 gas analyzer it's alittle tough, but can be done. I'm a smog tech in California, and have diagnosed most of them without having to resort to a pressure/smoke tester.
First, visually inspect all the hoses from the fill to the canister. Luckily, GM has hard line down the frame rail, and up to the canister. Unless that has rusty holes in it , I've never seen them leak. Leaving only about 3 or 4 inches of hose at the canister. Pull the bed, and disconnect the fill neck from the fill well, leaving the neck on the hose. Check the fill hose for cracks, and the tank vent hose from the pump module to the hard line on the frame.
If you find nothing there, now it's time to use your nose. I'd just use the gas analyzer and look for high HC readings waving and poking the probe around. But you probably don't have that optiion. Start smelling around the top of the pump module for fuel. It helps if you do it on a hot day.
If none of that bears fruit. Take off the lock ring on the pump module, pull it and inspect the O ring.
If cracked/split replace.
Most of the time, on GMT 400s, I find the module seal, O ring, is cracked or torn. The #1 reason that happens, besides age and mileage. Is that someone replaced the pump module, and did not lube the O ring during installation. Or forgot to clean the O ring groove on the tank, and the base of the flange.
The O ring ALWAYS needs to be lubed with SILICONE grease, prior to installation. Do not use white, or wheel bearing grease, silicone only. Not spray, grease.
If after inspecting everything, if you didn't find anything, the it will need to smoke tested. Also, don't just replace a tank out of hand. I've never seen a tank leak unless rust or collision damage put a hole there. Also, most tank leaks would show during filling or leave a puddle.
Anyone in California too, the state has a Repair Assistance Program. Too help people fix their car if it fails a smog check during registration renewal. They'll pay up to $500 in repairs. You can check it out
@ BAR.ca.gov under the Consumer Assistance Program.